In general, as shown in FIGS. 1 and 2, a lithium ion polymer battery 1, also referred to as a “pouch battery”, includes: a main casing body 2 having an inner space 2a of a predetermined size; a cover 3 coupled rotatably to the main casing body 2; a predetermined number of electrode assemblies 4 inserted in the inner space 2a of the main casing body 2, the electrode assembly including a cathode plate 4a, an anode plate 4b and a separator 4c; tabs 5 extending longitudinally and outwardly from the ends of the cathode plate 4a and the anode plate 4b of the electrode assemblies 4; and a cathode terminal 6 and an anode terminal 7 connected to each tab 5.
Additionally, in the top edge of the inner space 2a of the main casing body 2, an extension portion 2b extending horizontally and outwardly by a predetermined width is formed for the purpose of heat fusion. Further, the central part of each of the cathode terminal 6 and the anode terminal 7 connected to the tab 5 is coated with an insulation tape 8 formed of a non-conductive material. The insulation tape 8 is aimed to prevent a short circuit between a heat fusion device (not shown) and electrode terminals 6,7, when the extension portion 2b of the main casing body 2 is fused with an edge portion 3a of the cover 3 by means of the heat fusion device.
The above-mentioned pouch type lithium ion polymer battery according to the prior art may be prepared by the method as described hereinafter.
First, a predetermined number of electrode assemblies 4 including the cathode plate 4a, the anode plate 4b and the separator 4c are inserted into the inner space 2a of the main casing body 2. Next, a predetermined amount of electrolyte is injected into the inner space 2a. 
In this state, the tabs 5 of each electrode assembly 4 are connected to the corresponding electrode terminals 6,7 coated with the insulation tape 8 at the central part thereof. Additionally, each electrode terminal 6,7 and the insulation tape 8 are partially protruded from the main casing body 2 and the cover 3.
Then, the cover 3 is caused to be in close contact with the main casing body 2. Next, the extension portion 2b of the main casing body 2 and the edge portion 3a of the cover 3 are sealed using the heat fusion device so as to prevent leakage of the electrolyte.
However, such a conventional pouch type lithium ion polymer battery has problems in that an extension portion formed at the top edge of a main casing body for housing a predetermined number of electrode assemblies (so that it can be heat-fused to the corresponding edge portion of a cover) is too large compared to the effective size of the electrode assembly, and that the outer circumference of the main casing body coupled to the cover is wrapped with a separate plastic casing, thereby increasing the whole size of battery.